This invention relates to power control apparatus which controls charging and discharging of a power-generating or rechargeable power supply such as a fuel cell, lithium secondary cell, nickel metal-hydride battery, lead-acid battery, and electric double layer capacitor.
When a plurality of storage means such as batteries are connected in parallel, series, or both or when a plurality of storage means of different types are connected in parallel, series, or both, currents flowing through the storage means are dependent upon voltages and impedances of the storage means.
Therefore, when the storage means which are connected in parallel, series, or both are charged or discharged at a time, the current or voltage value of a certain storage means may exceed a permissible value.
To solve such a fault, prior arts have employed a method of controlling charging or discharging of the storage means with the minimum of currents that can flow through the storage means instead of charging or discharging with a total of currents that flow through all parallel-connected storage means (n pieces).
Japanese Application Patent Laid-Open Publication No. 2002-142353 discloses a method of disconnecting a faulty storage means when its current or voltage goes above a permissible value.
FIG. 9 shows a conventional method of controlling charging and discharging storage means. In FIG. 9, two or more sets 7 of series-connected batteries 1 are connected in parallel. Each set 7 of series-connected batteries 1 further comprises a means 9 for detecting a fault such as a micro short-circuit of each battery 1, a current bypass circuit 3 which comprises a current control means (switch) 4 and a resistor 5 and is connected to the battery set 7 in parallel with the set 7, and a fuse 6 which is connected in series to the bypass circuit 3 and the battery set 1 to electrically shut off the circuit when an overcurrent takes place.
When faults such as a micro short-circuit occur in a battery 1, it is detected by its voltmeter 2. The fault detecting means 9 receives a signal from the voltmeter 2 and closes the switch 4 to flow a large current through the current bypass circuit 3 which is connected in parallel to the faulty battery 1. This large current blows off the fuse 6. With this, the faulty battery is disconnected from the other non-faulty battery sets.
Japanese Application Patent Laid-Open Publication No. 2001-185228 discloses a system comprising two or more parallel-connected battery modules each of which has two or more secondary batteries connected in series. A current detecting circuit and a switch are connected in series to each battery module.
When one of the current detecting circuits detects an abnormal current value or direction, a control unit opens a switch of the battery module containing a faulty battery to disconnect the faulty battery module from the other non-faulty battery modules.
Japanese Application Patent Laid-Open Publication No. 08-88944 discloses a system which connects a plurality of cells each of which is a secondary battery or a plurality of battery modules each of which comprises two or more secondary batteries in series, parallel, or both. This system detects the voltage and the current of each cell or module and calculates the quantity of charge.
The system selectively charges cells or modules according to the result of calculation.